In a mobile communication system using VHF or UHF band frequencies, it is common for the frequencies to be multichannel and wide band. In this case, there is a strong requirement to decrease the transmission strength of spurious waves and to decrease noises in sideband, especially in the transmitting output signal in order not to disturb other communication systems.
On the other hand, due to the multichannel requirement of the communication system, the "phase synchronizing type digital frequency synthesizers" being easily obtainable, a very large number of frequencies are increasingly used as the signal source of the local oscillation frequency of the transmitter and the receiver. For such purpose, derives the local oscillation frequency signal source for the transmitter and for the receiver from a single phase synchronizing type frequency synthesizer widens the frequency bandwidth.
Such a device is basically constructed to have a phase synchronizing type of digital frequency synthesizer, a transmitter, a receiver, an antenna duplexer, and an antenna terminal. Further, in more detail, the transmitter comprises a side step oscillator, a phase or frequency modulator, a transmitting buffer amplifier, a frequency mixer, a bandpass filter, a preamplifier and a power amplifier. The receiver comprises, in more detail a receiving buffer amplifier, a receiving high frequency portion, an intermediate frequency converter, an intermediate frequency bandpass filter and a demodulator.
In this formation or arrangement of the transmitter, it is difficult to obtain a good signal having low noises and sufficiently suppressed spurious waves over a wide band at the transmitter output so that it has disadvantages of many technical and manufacturing problems.